Experimental analysis of the psychological effect of head injury

by Gronwall, D. M.

Abstract (Summary)

The purpose of this study was to investigate the immediate consequences of concussion. Previous work had either concentrated on memory defects only, included cases of cerebral damage as well as concussion, or examined residual defects persisting after the period of impaired consciousness had ended. It was hoped to determine which function or functions might be affected in concussion by testing only young adult cases of 'pure' concussion in the immediate post-traumatic period. In the main experiment a paced serial addition task was administered to a mildly concussed (MC) and seriously concussed (SC) group at twenty-four-hourly intervals during the hospital period, and thirty to forty days after discharge. A normal control and hospital control group were given the task at similar time intervals. Recent concussion impaired performance and SC Ss needed almost five times as long as controls to process each correct response while MC Ss were about twenty per cent slower, However, responses were qualitatively similar in all groups, and concussed Ss differed only in producing many more late response errors. At retest the MC group had regained control level, but although SC Ss had significantly improved PASAT scores they were still poorer than the other three groups. Experiments II and III investigated stages in the information transmission process which may have produced restricted information processing shown by PASAT results. Reaction and movement times were not longer than normal, although central processing time was. MC Ss did not have significantly slower non-symbolic RTs, or symbolic two- and four-choice RTs, but they differed significantly from controls on eight- and ten-choice symbolic trials. Again this difference between groups was not found at retest four weeks later. Results suggested inefficient 'pigeon-holing' (Broadbent, 1971) as a possible factor in reduced information transmission following concussion. However, a message repetition task indicated no difference between concussed and non-concussed Ss in use of this mechanism. Message repetition also demonstrated that patients had no difficulty in auditory perception of verbal material. In the third stage, normal Ss were given message repetition with and without a concurrent distracting task. Performance during distraction was sufficiently similar to that of recently concussed Ss to suggest that the patient group may have been poorer than controls on the same task only because they also had reduced processing capacity. When given PASAT with a secondary paced task, performance of another group of normal Ss was almost identical to concussed Ss in the first experiment. Finally, to test the possibility that reduced processing capacity was the result of increased distractability, that is, processing task-irrelevant stimuli, an attention task (speech shadowing) was given to a small group of MC Ss and normal controls. There were no instances of intrusions or interference from an irrelevant message to indicate a defect in selective attention, although MC Ss had significantly lower shadowing scores. It was concluded that reduction in processing capacity produced by concussion was a function of patients' lower level of arousal, and that performance resembled that reported in the literature from sleep-deprived Ss and cases of brain-stem damage or dysfunction. A feature of results was the extremely competent performance exhibited by concussion patients, given a reduction in total capacity. Similar optimizing behaviour was evident during distraction tasks, and it was suggested that ability to monitor and control distribution of available processing space by instructions ('set') is a general characteristic of ordered behaviour. This ability was not disturbed by degrees of concussion sustained by experimental Ss in this study. Amnesic symptoms of the immediate post-traumatic period were considered in terms of lowered arousal level. It was proposed that these might be explained by a combination of two factors: (i) processing space insufficient to store items while responding to them, and (ii) tagging of items in storage with levels of concurrent background activity, and thus 'state-dependent' memory. Evidence for a processing deficit existing after termination of the period of PTA was reviewed, and the possibility of permanent effect in terms of increased disability following repeated concussions. Some aspects of results important in considering rehabilitation programmes for head-injured patients were noted.